ElementType Find( List L, int m )
{
    int j=0, i;
    List a=L->Next;
    while(a)
    {
        j++;
        a = a->Next;
    }
    i = j-m+1;
    if(m<1||m>j)
    {
        return ERROR;
    }
    int x = 0;
    a=L->Next;
    while(a)
    {
        x++;
        if(x == i)
        {
            int b = a->Data;
            return b;
        }
        a = a->Next;
    }
}
